A woodlouse goes through three broad life stages: egg, juvenile (manca) and adult. The female carries her fertilised eggs in a brood pouch on her underside for several weeks; the young then emerge as miniature mancae, grow through a series of moults over roughly three months to reach adult size, and most live two to three years. This guide walks through each stage, how woodlice reproduce, and the role they play once they're grown.
Woodlice are the terrestrial members of the order Isopoda — crustaceans, not insects — so this life cycle is shared, in its essentials, by the tropical isopods kept in the hobby. If you'd like the broader picture first, see our overview of what isopods are.
The Egg Stage
Every woodlouse begins as a fertilised egg carried by the female in a fluid-filled brood pouch (the marsupium) on the underside of her body. This is a feature woodlice share with their wider crustacean group, the peracarids: rather than laying eggs in the environment, the female keeps them in a protected, portable pocket of moisture where they're shielded from drying out and from predators.
A single brood is often in the region of a few dozen eggs, though the number varies by species and the size of the female. The eggs develop inside the pouch over several weeks before the young are ready to emerge — a slow, sheltered start that gives a good proportion of each brood the chance to survive.
Juvenile Development (Mancae)
Newly emerged woodlice are called mancae, and they look like pale, miniature adults with one important difference: they leave the pouch with only six pairs of legs rather than the adult's seven. They gain that final pair, along with the last body segment, after their first moult — usually within a day or so of emerging. This is one of the easiest ways to tell a very young woodlouse from an adult.
From there, growth happens through repeated moulting. Like all crustaceans, a woodlouse has a rigid exoskeleton that can't expand, so to get bigger it must shed the old shell and harden a new, larger one. Woodlice do this in two halves — shedding the rear of the body first, then the front a few days later — which is why a half-pale woodlouse is mid-moult, not unwell. (We cover this in depth in our guide to isopod moulting.) It takes roughly three months of these moults for a young woodlouse to reach adult size.
The Adult Woodlouse
Adult woodlice are small crustaceans, often mistaken for insects, with fourteen legs and a segmented, plated body. Most species reach maturity within about a year and live two to three years, though some individuals in good conditions live longer.
Reaching adult size doesn't stop the moulting — woodlice continue to shed and replace their exoskeleton throughout life, even though size gains become minimal once they're mature. Because that exoskeleton is reinforced with calcium, a steady calcium supply matters at every stage, which is why keepers provide cuttlebone in captive setups.
How Do Woodlice Reproduce?
Courtship in woodlice is surprisingly involved. A male signals his readiness by climbing onto the female's back and tapping or "drumming" on her with his legs and antennae before mating, with sperm transfer taking only a few minutes. After fertilisation, the female carries the developing eggs in her brood pouch until the young emerge — completing the cycle.
One myth worth correcting: woodlice are sometimes said to reproduce by parthenogenesis (females cloning themselves without males). This is true of a small number of species — notably the common pygmy woodlouse, Trichoniscus pusillus — but it is not how woodlice reproduce in general. The vast majority, including the familiar pill and rough woodlice, reproduce sexually.
Where Do Woodlice Live?
Woodlice need moisture and shelter, so they gather wherever it's damp and dark: under logs and stones, in leaf litter and rotting wood, and in compost heaps and shady corners of gardens. These spots offer both the humidity their gill-like breathing structures depend on and a ready supply of the decaying matter they eat.
They're also remarkably adaptable as a group — woodlice as a whole are found from gardens to grasslands and even into semi-arid environments — but as individuals they remain tied to damp microhabitats, retreating to them whenever conditions dry out. In the keeping hobby, recreating that damp, sheltered environment with a suitable isopod substrate and hiding places is the foundation of good care.
Their Role in the Ecosystem
Woodlice are detritivores: they feed on dead and decaying plant matter, fungi and rotting wood, breaking it into smaller fragments that decompose far faster and return nutrients to the soil. This quiet recycling supports plant growth and soil health, and it's exactly the service that makes isopods so valuable as cleanup crews in bioactive terrariums.
They also sit near the base of the food web, providing food for birds, amphibians, reptiles and predatory invertebrates. Some predators specialise in them — woodlouse spiders of the genus Dysdera have jaws shaped specifically for tackling their armoured prey, and predatory flatworms hunt them too. Newly emerged mancae, with their softer shells, are especially vulnerable.
Common UK Woodlouse Species
Britain has around 35 to 40 native woodlouse species. Three of the most frequently encountered are:
- Common pill woodlouse (Armadillidium vulgare) — the species that rolls into a tight ball when disturbed, growing to around 18 mm. The hobby's many Armadillidium morphs descend from this group.
- Common rough woodlouse (Porcellio scaber) — grey with a matt, slightly bumpy texture, up to about 17 mm, and the wild ancestor of many Porcellio colour forms in the hobby.
- Common pygmy woodlouse (Trichoniscus pusillus) — tiny at around 5 mm and purplish-red, yet probably the most abundant woodlouse in Britain.
A Note on Woodlice Indoors
Woodlice indoors are a sign of damp rather than a pest problem in their own right. They don't bite, spread disease, or damage sound, dry timber, and they can't survive long in a dry home. If they keep appearing, the lasting fix is to address the moisture — repairing leaks, improving ventilation and sealing gaps at ground level — and any you find can simply be returned to a damp, sheltered spot outside.
Frequently Asked Questions
How long do woodlice live?
Most woodlice live two to three years, with some individuals reaching longer in good conditions. They reach breeding maturity within about a year and continue moulting throughout life.
How many eggs do woodlice lay?
A female carries a brood of eggs — often a few dozen, varying by species and her size — in a fluid-filled pouch on her underside, where they develop for several weeks before the young emerge.
What is a baby woodlouse called?
A newly emerged woodlouse is called a manca. Mancae look like pale miniature adults but have only six pairs of legs, gaining the seventh pair after their first moult.
How long does a woodlouse take to grow up?
Roughly three months from emerging as a manca to reaching adult size, achieved through a series of moults, after which it typically matures within its first year.
Do woodlice reproduce without mating?
A few species can — the common pygmy woodlouse reproduces parthenogenetically — but most woodlice reproduce sexually, with the female carrying fertilised eggs in her brood pouch.
What do woodlice eat?
Decaying plant matter, leaf litter, rotting wood and fungi. By breaking this material down, woodlice recycle nutrients into the soil, which is why they're valued as decomposers and bioactive cleanup crews.
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